Every situation requires a different approach. When we are walking around and our phones are in our pockets or backpack, our notification volume must be loud in order to be heard over the loud noises of the outside world. But when we're at home, notification sounds don't need to be nearly as loud in order to be heard.

To achieve the desired goal, which is having loud notifications outside and quiet ones inside, you can use an application like Tasker. Configuring Tasker isn't easy, and there are more accessible applications like one by XDA Forum Member Sanryd. This simple tool allows you to set a separate notification volume for when your phone is asleep and when it is awake. After a few simple steps, you will be able to adjust the volume level to suit your needs. If you don't like the application's presets, you can easily modify them. It's a very simple application, so it doesn't require any special privileges like root or new OS versions.

You can get the latest version from the original thread, so head over there to give Awake/Sleep Volume Adjuster a shot.